Impact of nanostructure on thermal transport in silicon nanowire

This thesis studies the effect of nanostructure on the thermal transport of one-dimensional silicon nanowire. We firstly demonstrate that the thermal conductivity of single-crystalline silicon nanowires can be even lower than that of amorphous silicon by introducing nanoscale porosity, with values as low as 0.33 W/m-K at 300K for 43% porosity. This can be attributed to: (a) reduction of group velocity due to increased surface-to-volume ratio and (b) diffusive scattering at the pore boundaries. The second part of this work studies the impact of point defects on thermal transport in silicon nanowires. The creation of a well-controlled distribution of point-defects into silicon nanowires was demonstrated in this work. By using helium ion irradiation, we show that the thermal conductivity of an individual silicon nanowire can be tuned between the crystalline and amorphous limits. Our study aims to provide a better understanding of phonon transport at nanoscale.